简单的UDP代码 客户端+服务器 （网络真好玩，发什么自动回复什么，还能查字典呢，一起来玩呀）

1.简单的UDP echo 服务器+客户端
发什么，回什么

服务器端的代码如下

package udp.echo;import java.net.*;public class Server{
public static void main(String[] args) throws IOException{
//新建一个DatagramSocket
DatagramSocket udpServerSocket=new DatagramSocket(9898);  //连接的同时直接绑定9898端口，如果一台主机有多个网卡，就需要绑定IP+端口
//接下来等着收消息
byte[] receiveBuffer=new byte[1024];//传过来的是二进制数据流，需要一个字节数组来接收
DatagramPacket receivePacket=new DatagramPacket(receiveBuffer,receiveBuffer.length);
udpServerSocket.receive(receivePacket);
InetAddress clientAddress=recievePacket.getAddress();
System.out.printf("我从 %s:%d 收到了消息%n",clientAddress.getHostAddress(),receivePacket.getport());
System.out.printf("我一共收到了%d字节的数据%n",receivePacket,getLength())
//需要将发过来的二进制数据流进行解码
String message=new String(receivePacket.getData(),0,receivePacket.getLength(),"UTF-8");
System.out.println(message);//收到消息了byte[] sendBuffer=message.getButes("UTF-8");
DatagramPacket sendPacket=new DatagramPact(sendBuffer,sendBuffer.length,clientAddress,receivePacket.getPort());
udpServerSocket.send(sendPacket);udpServerSocket.close();  //最后要关闭连接
}

客户端的代码如下：

package udp.echo;import java.net.*;public class Client{public static void main(String[] args) throws IOException{//建立连接DatagramSocket clientSocket=new DatagramSocket(); //客户端不需要绑定端口啥的，直接发送数据String message="收到我的消息没？";//需要将这个文本转成字节型的byte[] sendBuffer=message.getBytes("UTF-8");//默认使用UTF-8编解码，但是推荐写上//构建DatagramPacketbyte[] serverIP=new byte[4];//地址是IPv4类型的，所以是4位//我要发送给本机，本机默认IP地址是127.0.0.1  改成别的主机的IP不同设备互动会更有意思哦(*^^*)serverIP[0]=127;serverIP[1]=0;serverIP[2]=0;serverIP[3]=1;InetAddress serverAddress=InetAddress.getByAddress(serverIP);DatagramPacket sendPacket=new DatagramPacket(sendBuffer,sendBuffer.length,serverAddress,9898);//客户端要带着IP和端口，知道自己往哪儿发，端口号要和服务器那边一致udpClientSocket.send(sendPacket);//发送数据byte[] receiveBuffer=new byte[1024];
DatagramPacket receivePacket=new DatagramPacket(receiveBuffer,receiveBuffer.length);
udpClientSocket.receive(receivePacket);
String responseMessage=new String(receivePacket.getData(),0,receivePacket.getLenth(),"UTF-8");
System.out.println("responseMessage");udpClientSocket.close(); //关闭连接

注意：1.无论是发送数据，还是接收数据都需要一个byte类型的数据，需要进行字节类型和字符类型的转换；
2.需要指定相同的编码方式；
3.服务器是先收后发，客户端是先发后收，其他都是类似的；
4.通过DatagramPacket 更加深入的理解UDP是面向报文的

2.把上面的代码稍加改动，就是一个查字典小工具啦

服务器的代码如下：

public class Server{
private static final Map<String,String> dict=new HashMap<>();
static{
dict.put("苹果","apple");
dict.put("梨","pear");
dict.put("桃子","peach");
dict.put("葡萄","grape");
dict.put("香蕉","banana");   //手动输进去有点low啊
}
public static void main(String[] args) throws IOException{
//新建一个DatagramSocket
DatagramSocket udpServerSocket=new DatagramSocket(9898);  //连接的同时直接绑定9898端口，如果一台主机有多个网卡，就需要绑定IP+端口
//接下来等着收消息
byte[] receiveBuffer=new byte[1024];//传过来的是二进制数据流，需要一个字节数组来接收
DatagramPacket receivePacket=new DatagramPacket(receiveBuffer,receiveBuffer,receiveBuffer.length);
udpServerSocket.receive(receivePacket);
InetAddress clientAddress=recievePacket.getAddress();
System.out.printf("我从 %s:%d 收到了消息%n",clientAddress.getHostAddress(),receivePacket.getport());
System.out.printf("我一共收到了%d字节的数据%n",receivePacket,getLength())
//需要将发过来的二进制数据流进行解码
String message=new String(receivePacket.getData(),0,receivePacket.getLength(),"UTF-8");
System.out.println(message);//收到消息了String responseMessage=dict.getOrDefault(message,"我也不知道呀");byte[] sendBuffer=responseMessage.getButes("UTF-8");
DatagramPacket sendPacket=new DatagramPact(sendBuffer,sendBuffer.length,clientAddress,receivePacket.getPort());
udpServerSocket.send(sendPacket);udpServerSocket.close();  //最后要关闭连接
}

客户端的代码如下：

package udp.echo;import java.net.*;public class Client{public static void main(String[] args) throws IOException{//建立连接DatagramSocket clientSocket=new DatagramSocket(); //客户端不需要绑定端口啥的，直接发送数据while(true){Scanner scanner=new Scanner(System.in); String message=scanner.nextline();byte[] sendBuffer=message.getBytes("UTF-8");//默认使用UTF-8编解码，但是推荐写上//构建DatagramPacketbyte[] serverIP=new byte[4];//地址是IPv4类型的，所以是4位//我要发送给本机，本机默认IP地址是127.0.0.1  改成别的主机的IP不同设备互动会更有意思哦(*^^*)serverIP[0]=127;serverIP[1]=0;serverIP[2]=0;serverIP[3]=1;InetAddress serverAddress=InetAddress.getByAddress(serverIP);DatagramPacket sendPacket=new DatagramPacket(sendBuffer,sendBuffer.length,serverAddress,9898);//客户端要带着IP和端口，知道自己往哪儿发，端口号要和服务器那边一致udpClientSocket.send(sendPacket);//发送数据byte[] receiveBuffer=new byte[1024];
DatagramPacket receivePacket=new DatagramPacket(receiveBuffer,receiveBuffer.length);
udpClientSocket.receive(receivePacket);
String responseMessage=new String(receivePacket.getData(),0,receivePacket.getLenth(),"UTF-8");
System.out.println("responseMessage");
}udpClientSocket.close(); //关闭连接

3.稍加改动就是一个聊天软件

聊天宝欢迎您嘞！